In the production of plate glass, a conveying mechanism for forming the plate glass from a molten state or for slowly cooling the formed glass plate is required. In general, the conveying mechanism is constituted by a conveying roll, and a disc roll has been used as one example of the conveying roll.
FIG. 1 is a schematic view showing one example of a disc roll 10, which is prepared by stamping out annular discs from a disc member base material which is obtained by forming, into a plate form having a thickness of several millimeters, an aqueous slurry in which an inorganic fiber, an inorganic filler, a binder, etc. are compounded; fitting these plurality of disc members 12 together on a metal shaft 11 acting as a rotary shaft by insertion to form a roll-shaped laminate; and fixing the laminate on the shaft with nuts 15 or the like with the interposition of flanges 13 arranged at both ends, with some compression applied to the disc members 12. The peripheral surfaces of the disc members 12 function as a conveying surface.
Then, the above-mentioned disc roll 10 is integrated, for example, into a plate glass production apparatus 100 as shown in FIG. 2, and used for molding and conveyance of plate glass. This plate glass production apparatus 100 is an apparatus for producing plate glass by continuously discharging a glass melt 110 from a linearly opened slit 102 of a melting furnace 101, allowing this discharged strip-shaped glass melt 110 to flow downward and to be cooled during the fall to harden it. The disc rolls 10 function as a pair of stretching rolls, which hold the strip-shaped glass melt 110 therebetween to forcibly send it downwards. It is therefore preferred that the disc roll 10 has, as well as heat resistance, some degree of flexibility so as not to damage a glass surface. A disc roll containing mica particles has been known (see Patent Document 1).
Patent Document 1: JP 59-028771 B
As shown in FIG. 2, a pair of the disc rolls 10 hold the strip-shaped glass melt 110 therebetween to forcibly send it downwards. However, the strip-shaped glass melt 110 is in a semisolid state, so that both ends of a conveying face tend to be conglobated by surface tension. Accordingly, the resulting plate glass is hardened with its center portion being thin, resulting in deteriorated flatness at both ends thereof. Further, only both ends of the disc roll 10 come into contact with the plate glass upon conveyance, and the plate glass breaks in some cases by stress concentration to the thick ends thereof.
Further, the disc roll 10 is constantly in contact with the high-temperature strip-shaped glass melt 110. By pressing both ends thereof in a high-temperature state for ensuring the surface pressure with the glass plate, thermal deformation of the shaft 11 occurs. As a result, the conveying surface also has an uneven surface following the shape of the shaft 11, so that contacts with the strip-shaped glass melt 110 take place only locally, thereby causing stress concentration to a part of the plate glass to break the glass plate or to scratch the surface thereof.
There is a tendency that the area of the plate glass to be produced is being increased. With that tendency, the conveying surface of the disc roll 10 increases in width, and the shaft increases in length. Accordingly, the influence by surface tension and the degree of deformation of the shaft 11 as described above also increase, and it has increasingly become difficult to uniformly apply force to the plate glass.
Such problems have not been solved by conventional disc rolls including the disc roll described in patent document 1, having flexibility imparted thereto.
Further, disc rolls become liable to wear out as flexibility is imparted thereto, resulting in a shortened life thereof. Further, in liquid crystal displays and plasma displays, quality requirements to plate glass are particularly severe, and it becomes a significant problem to prevent contamination of the surface thereof caused by abrasion powder (powder omission) from the disc roll. The disc roll in which importance is attached to flexibility is liable to wear out, so that the powder omission is liable to occur, which tends to result in a reduced yield.
In order to impart flexibility to the disc roll, it is also possible to reduce the pressure applied at the time when the disc members 12 are loaded on the shaft 11 and compressed from both ends, to thereby lower the compressed density. However, such reduced pressure adversely affects the durability of the roll, resulting in a shortened roll life.